Pathogenic Th17 cell, as a special Th17 cell subset, triggered and aggravated the immune response of chronic inflammatory diseases, such as periodontitis, IBD, and rheumatoid arthritis, through IL-17, IL-21, IL-22, IL-23, and GM-CSF (gene: CSF2) [5, 32–34]. This evidence concerns the gene IL21 and periodontitis.